1. Field of the Invention
This invention relates to power plants and more particularly to electricity producing power plants utilizing fuel cells as the power source.
2. Description of the Prior Art
In the fuel cell art there have been three general approaches to improving fuel cell performance. One approach is to increase the temperature at which the fuel cell operates. This approach, however, is limited by material corrosion and, in acid electrolyte cells, by acid evaporation. A second approach is to attempt to increase the amount of catalyst per square inch of electrode surface area. This approach, however, is limited by the increased expense and practical limitations in the amount of catalyst that can be possibly be put on a certain area of electrode. A third approach is to increase the pressure of the reactants within the fuel cell. It is well known in the art that fuel cells perform better as reactant pressures increase. One of the major stumbling blocks to this approach is that it requires cnsiderable energy to pressurize the reactants. It has been considered, for example, that the energy to pressurize reactants should be the electrical energy produced by the fuel cell; that electrical energy would be used to drive a compressor. The problem is that it takes about 30% of the electrical output of the cell stack to drive a compressor to produce a reasonable reactant pressure. This means that the fuel cell would have to be increased in size by about 50% to make up for the loss of usable electrical power. Since a fuel cell stack is itself the most expensive component of a fuel cell power plant, the increase in performance is offset by the increased cost due to increased cell size. Because total electrical power output of the cell stack is increased, other components of the power plant will have to be increased proportionately such as the condensing apparatus and the fuel conditioning apparatus. This further increases size and cost of the power plant. Further, other apparent disadvantages in the power plant system utilizing high pressure reactants are the cost of additional equipment to pressurize the reactants, the necessity for more expensive sealing arrangements, and the additional cost due to the necessity of utilizing stronger components to contain the higher pressures. In view of the foregoing considerations, with regard to power plants utilizing air as the oxidant, it has always been considered that no net advantage could be achieved, and most likely, there would be a net disadvantage in going to power plants utilizing high pressure reactants in the fuel cell stack. For the foregoing reasons, up to the present time, these fuel cell power plants have always used reactants at atmospheric pressures.